The invention relates to absolute, relative and differential pressure sensors having a metal diaphragm facing the process. More specifically, the invention relates to a pressure sensor for mounting in a process connection.
A pressure sensor having a metal diaphragm facing the process comprises a housing with a passage whose process-side opening is closed by a metal diaphragm The deformation member of a pressure transducer is arranged at the opening, averted from the process, of the passage. The passage is filled with a transmission liquid which transmits the pressure present at the diaphragm to the deformation member of the pressure transducer, the pressure transducer generating a measuring signal owing to the pressure-induced deflection of the deformation member.
There are a multiplicity of variants of such pressure sensors with a metal diaphragm facing the process. The number of possible variants is yielded as the product of the number of process connections or connecting elements and the number of basic sensors or pressure sensor elements. The latter is given as the product of the number of measuring ranges and the number of process diaphragm materials, and the number of different transmission liquids.
Several thousand variants are easily yielded for a pressure sensor family. Storing all the variants is very complicated and expensive and is therefore to be avoided. To the extent that the number of process connections frequently constitutes the largest factor, an obvious approach is to prefabricate the pressure sensor elements of one family and keep them in store already calibrated. Depending on what is required, a pressure sensor element is then welded to an appropriate connecting element.
It turns out to be difficult in this case to connect the pressure sensor element reliably to the connecting element without putting the calibration at risk. As illustrated in FIG. 3, when the pressure sensor element 110 is being welded into the connecting element 140 the welding scam 150 must be designed to be solid and deep in order to withstand the process pressure and any instances of overload shock pressure.
This contradicts the requirement to configure the welding seam as thin and flat as possible so that no mechanical stresses are introduced into the active region of the process diaphragm 120, because only thus is it possible to dispense with renewed calibration of the pressure sensor element.
The object of the invention is to provide a pressure sensor element which can be welded in a connecting element without repercussions and without making compromises in the process with regard to pressure resistance or sensor performance.
The object according to the invention is achieved by a pressure sensor arrangement having: a pressure sensor element comprising a pressure transducer element for outputting a pressure-dependent signal; and an isolator member having a passage between a first opening in an end face of the isolator member which extends essentially perpendicular to the mounting direction of the pressure sensor element as far as its outer edge, and a second opening in a second surface of the isolator member, the pressure transducer element being connected to the passage through the second opening, a diaphragm which seals the first opening of the passage, and a transmission medium in the passage for the purpose of transmitting the pressure present at the diaphragm to the pressure transducer element, wherein the diaphragm extends laterally or radially outward beyond the outer edge of the end face of the isolator member; a connecting element with an opening in a surface for holding the pressure sensor element, the pressure sensor element being fixed in the opening in such a way that the end face of the isolator member lies in a plane with the edge region of the surface about the opening, the projecting region of the diaphragm being connected to the edge region of the surface along an inherently closed connecting seam about the opening; and a diaphragm ring with an inner edge region and an outer edge region, the inner edge region being fastened on the end face of the isolator member by means of an inherently closed seam of the isolator member and the outer edge region being fastened on the surface of the connecting element by means of an inherently closed seam about the opening. Further advantageous aspects of the invention follow from a consideration of the claims, the the description and the drawings.
The pressure sensor element according to the invention for mounting in a connecting element comprises:
a pressure transducer element for outputting a pressure-dependent signal; and a isolator member having a passage between a first opening in an end face of the isolator member which extends essentially perpendicular to the mounting direction of the pressure sensor element as far as its outer edge, and a second opening in a second surface of the isolator member, the pressure transducer element being connected to the passage via the second opening, and a diaphragm which seals the first opening of the passage, and a transmission medium in the passage, for the purpose of transmitting the pressure present at the diaphragm to the pressure transducer element, the diaphragm extending laterally beyond the outer edge of the end face of the isolator member.
In order to provide pressure sensor arrangements, the pressure sensor element according to the invention can be mounted in suitable connecting elements without repercussions, i.e. the calibration of the pressure sensor element is maintained during the mounting.
In a preferred embodiment, the basic sensor element is screwed into an opening in the connecting element, which is designed as a process connection. In this case, a gap can remain between the pressure sensor element or the isolator member of the pressure sensor element and the connecting element, and be covered by the diaphragm. The diaphragm is then fastened along its outer edge on the connecting element.
The fastening is preferably designed as an inherently closed connecting seam, in particular as a welding seam, but it is also possible to provide soldering seams or bonding seams.
The seam need not transmit the total pressure force present at the opening if the sensor element is fixed in the opening of the connecting element and the diaphragm region enclosed by the connecting seam is sufficiently elastic.
It is therefore possible for the fastening, for example by welding, to be of a weak enough design that the calibration of the pressure sensor element is maintained.
In a further aspect, the solution according to the invention is modified to the effect that instead of a pressure sensor element with a projecting diaphragm a pressure sensor element with a conventional diaphragm whose circumference runs completely on the end face of the isolator member. In this case, an additional diaphragm ring is provided however. The pressure sensor element is arranged in an opening in a mounting surface of a connecting element, and the diaphragm ring is fastened on the one hand with the aid of an inherently closed seam of the isolator member on the end face of the isolator member and, on the other hand, with the aid of an inherently closed connecting seam about the opening on the mounting surface.
In order to fix the pressure sensor element, it is generally self-closed, force-closed or friction-closed connections between the isolator member and the connecting element which are suitable, self-closed connections being preferred.
In order to fix the pressure sensor element, it is generally self-closed, force-closed or friction-closed connections between the isolator member and the connecting element which are suitable, self-closed connections being preferred.